Re: [PATCH v2] iio: chemical: scd30: Replace manual locking with RAII locking

[Jonathan Cameron <jic23@kernel.org>]

On Tue, 19 May 2026 08:19:43 -0500
Maxwell Doose <m32285159@gmail.com> wrote:

> scd30_core.c currently uses manual mutex_lock() and mutex_unlock()
> calls. Replace them with the newer guard(mutex)() for cleaner RAII
> patterns and to improve maintainability.
> 
> Add new helper function scd30_trigger_handler_helper_locked() containing
> the critical section for scd30_trigger_handler().
> 
> In addition, small refactor to replace "?:" operator with regular
> if/else returns.
> 
> Signed-off-by: Maxwell Doose <m32285159@gmail.com>
Hi Maxwell

One of those cases where it made us look at code for first time in a while.
The original handling merrily copied garbage data.  Let's clean that up whilst
we are here.

Thanks,

Jonathan
>  static IIO_DEVICE_ATTR_RO(sampling_frequency_available, 0);
> @@ -579,24 +587,34 @@ static irqreturn_t scd30_irq_thread_handler(int irq, void *priv)
>  	return IRQ_HANDLED;
>  }
>  
> +/* Meant ONLY for scd30_trigger_handler() */
> +static int scd30_trigger_handler_helper_locked(struct iio_dev *indio_dev,
> +					       int *scan_data, int arr_size)
> +{
> +	struct scd30_state *state = iio_priv(indio_dev);
> +	int ret;
> +
> +	guard(mutex)(&state->lock);
> +
> +	if (!iio_trigger_using_own(indio_dev))
> +		ret = scd30_read_poll(state);
> +	else
> +		ret = scd30_read_meas(state);
> +	memcpy(scan_data, state->meas, arr_size);

Why is that a good thing to do if we are in an error condition?
I've have thought the data wasn't valid.

	if (ret)
		return ret;

	memcpy()..

	return 0;

Or is there something useful in that data?
Looks like some less than ideal code in the original driver but
I think it makes sense to clean that up now. Just make sure to put
a note in the patch description.





> +	return ret;
> +}
> +
>  static irqreturn_t scd30_trigger_handler(int irq, void *p)
>  {
>  	struct iio_poll_func *pf = p;
>  	struct iio_dev *indio_dev = pf->indio_dev;
> -	struct scd30_state *state = iio_priv(indio_dev);
>  	struct {
>  		int data[SCD30_MEAS_COUNT];
>  		aligned_s64 ts;
>  	} scan = { };
>  	int ret;
>  
> -	mutex_lock(&state->lock);
> -	if (!iio_trigger_using_own(indio_dev))
> -		ret = scd30_read_poll(state);
> -	else
> -		ret = scd30_read_meas(state);
> -	memcpy(scan.data, state->meas, sizeof(state->meas));
> -	mutex_unlock(&state->lock);
> +	ret = scd30_trigger_handler_helper_locked(indio_dev, scan.data, sizeof(scan.data));
>  	if (ret)
>  		goto out;
>